1. Field of the Invention
This invention relates in general to a new and useful method and apparatus for producing blank material of uniform weight per piece and cross-section of a metal particularly a steel and wherein the ingot is produced by bottom pouring into a vertically elongated mold at a relatively slow rate.
2. Description of the Prior Art
The fabrication of many rotation-symmetrical parts on shaping machines is in part semi-automated or fully automated and therefore requires starting material of uniform weight per piece and of uniform cross-section, as for example: rings, railroad wheels, car tires, containers, tubes, etc. It is known practice to produce such blank material by casting the steel in conical molds, rolling out or forging out the resulting conical ingot to obtain a uniform cross section having a good surface quality, and subsequently dividing the shaped ingot into sections of equal length. This known method does indeed furnish satisfactory blank material, which because of the uniform cross section can well be processed further and can easily be divided into blank material of equal weight by division into sections of equal length. However, it is a disadvantage that the cast ingot must be subjected to an additional shaping operation.
It is further known to cast conical long ingots and to use these ingots without further shaping after their division into sections of equal weight for further processing in ring rolling mills. The disadvantage of this method is that because of the different cross-sections required, the sections must be cut in unequal lengths and it is difficult to maintain the required uniformity of weight. Moreover, use in semi-automatic or fully automatic systems often precludes a variable cross-section of the blank material. It is further known to cast individual ingots and to use them for ring production without further division or shaping. This method is generally uneconomical, as the expense in casting, cleaning (polishing) and transportation is higher and the yield less favorable than for the long ingot (Stahl and Eisen 79 (1959) p. 1913 ff).
Taking this state of the art as point of departure, the problem of the invention is seen in the fact that for the part, full or semi-automatic further processing, such as rolling in a ring rolling mill or fabrication of tubes or containers on a shaping machine, it is important that the blank material should, at equal length, have equal weight and also equal cross-section of each individual section size, and it is difficult to produce these, without rolling or forging deformation, in a quality insuring their destruction-free processing.
The known molds are generally designed conical to facilitate the stripping of the solidified ingots. There has also been produced a heavy ingot form of a weight of 114 t and a length of 5.20 m with equal cross section over the entire length, as it was expected that, due to their great diameter the ingots to be cast, would shrink sufficiently so that they could be pulled out of the iron mold even without taper (Stahl and Eisen (1922, p. 653). Nothing has been reported about the behavior of this mold in casting. It is stated in "Stahl und Eisen" 1931, on page 1225, left column, that for the downwardly widening mold as little conicity as possible is desirable. A conicity of 1.3 and down to 0.7 is regarded as sufficient to avoid difficulties in stripping. Experiments with parallel walled molds are also being carried out. Besides, for molds of equal cross section over their entire length the removal of the cast ingot is made possible by longitudinal division of the molds (e.g. German Pat. Nos. 95,515, 67,035). While such longitudinally divided molds facilitate the removal of the ingots, they may easily lead to elevations on the ingot (burrs) at the points of division by inflow of the liquid metal during pouring. Due to this defect, the material cast in longitudinally divided molds is usable as blank material for further processing only with qualifications or only after considerable polishing (cleaning), since at these points it may easily lead to bursting or overrolling during upsetting, stretching and rolling in axial direction. Further, divided molds, in particular in the case of long ingots, are unfavorable because of the susceptibility of warping with the difficulty of sealing the point of division during casting. The high cracking susceptibility in conventionally poured ingots of circular cross-section as against those with polygonal cross section or corrugated surface, and the difficulties in stripping to be expected for ingots of equal cross-section over their length, have until now led to the result that no ingots are poured with equal cross-section over the length, in particular with round cross section.